1. Field of the Invention
The present invention relates to a winding configuration of a magnetic head used for a magnetic field modulation type magneto-optical disk drive and a drive circuit for the magnetic head.
2. Description of the Prior Art
A magnetic field modulation type magneto-optical disk drive has a higher recording density than other optical recording media and can transmit data in a high speed, so it is regarded as a main stream of various recording media in digital information society. In order to utilize the superior transmission speed, it is important that a magnetic reversal speed of a magnetic head becomes fast.
A typical magnetic head and a drive circuit for the same in the prior art are disclosed in Japanese unexamined patent publication No. 52-46807 for example, in which a magnetic head having a bifilar winding is driven by a constant-current circuit.
FIG. 1 shows a schematic structure of a magnetic head having a bifilar winding. FIG. 2 shows the winding configuration of the magnetic head. This magnetic head has an E-type core 11 and windings L1 and L2 wound on the core 11. The winding L1 and L2 are wound in the same winding direction. In other words, the entire winding (L1+L2) from the tap a to the tap c has a center tap b.
Using the magnetic head having the above-mentioned bifilar winding, the polarity of the magnetic field generated by the magnetic head can be switched easily without changing the direction of the current flowing through the constant-current circuit. In FIG. 1 for example, the current always flows into the center tap b and flows out of tap a or c. One of the current paths connected to the taps a and b is turned on selectively so that one of the windings L1 and L2 is magnetized selectively, and the polarity of the magnetic field generated by the magnetic head is switched. This switching of the current path can be performed by using a common emitter type drive circuit that enables high speed switching. The common emitter type drive circuit has been used widely in a drive circuit for a magnetic core memory device, for example.
However, this drive circuit for a magnetic head having a bifilar winding cannot use the winding effectively since only one of the windings L1 and L2 is used for generating a stationary magnetic field during the period without the magnetic reversal. In addition, a power consumption of the drive circuit is large.
A number of methods for reducing the power consumption of the drive circuit are proposed. For example, an H-type switching circuit is disclosed in Japanese unexamined patent publication No. 63-94406, or a resonance type circuit is disclosed in Japanese unexamined patent publication No. 1-130302. However, a limit of performance about a switching delay of a semiconductor device and a limit of operational frequency appeared, and the current drive circuit is receiving an attention again.
The differential di/dt of a current flowing through the winding of the magnetic head is proportional to a voltage E applied to the winding as shown in the following equation.
xe2x80x83di/dt=E/L
Here, L is an inductance of the winding.
Therefore, for increasing the differential di/dt so as to switch the magnetic field quickly, it is necessary to increase the voltage E that is applied to the winding. However, during the period without the magnetic reversal, it is enough to maintain a direct current flowing through the winding. Namely, if the voltage E that is applied to the winding is increased too largely, the waste of power consumption increases in the constant-current circuit during the period without the magnetic reversal.
A method for avoiding this waste of power consumption is disclosed in Japanese unexamined patent publication No. 8-45008 or No. 8-96435, in which the voltage is raised only when switching the current (i.e., when the magnetic field is reversed) and otherwise, a relatively lower voltage is applied to the winding. However, this method also cannot decrease the power consumption of the constant-current circuit sufficiently, and a further improvement is desired.
There is another method proposed in Japanese unexamined patent publication No. 7-182717 or No. 5-225501, in which the winding is divided into several elements so as to generate magnetic fields in parallel. However, even if the parallel winding elements can bring an effect of a high speed magnetic reversal, it does not contribute the decrease of the power consumption of the entire circuit including the constant-current circuit.
The object of the present invention is to provide a drive circuit that can reduce the power consumption in the constant-current drive circuit. Another object of the present invention is to provide a winding configuration of the magnetic head that is suitable for the drive circuit.
A drive circuit according to the present invention drives a magnetic head that has a bifilar winding with a center tap and is used for a magneto-optical disk drive.
According to a first aspect, the drive circuit applies a first magnetizing voltage between the center tap and one of the winding ends of the bifilar winding so as to magnetize only half of the winding during a first period in which a magnetic reversal occurs, and applies a second magnetizing voltage between the winding ends of the bifilar winding so as to magnetize the entire winding during a second period in which a magnetic reversal does not occur. Thus, the drive circuit can save the power consumption by reducing the magnetizing current during the period without a magnetic reversal.
Preferably, the second magnetizing voltage applied to the winding ends of the bifilar winding during the second period is set lower than the first magnetizing voltage applied to the center tap and one of the winding ends of the bifilar winding during the first period. Thus, the power consumption is further reduced. In addition, the switching from the second magnetizing voltage to the first magnetizing voltage is preferably performed before the magnetic reversal, so as to enable a high-speed magnetic reversal.
As a concrete configuration, each of the winding ends of the bifilar winding is connected to a magnetizing current path that includes two current paths connected in parallel, each of the two current paths has a switching device, and the switching devices are controlled so that the magnetizing current can flow through the two current paths during the first period in which a magnetic reversal occurs and can flow through one of the two current paths during the second period in which a magnetic reversal does not occur. Thus, the circuit that can perform the high speed magnetic reversal is simplified.
According to a second aspect, the drive circuit applies a first magnetizing voltage between the center tap and one of the winding ends of the bifilar winding so as to magnetize only half of the winding during the data writing period with a magnetic reversal, and applies second magnetizing voltage between the winding ends of the bifilar winding so as to magnetize the entire winding during the data reading period. In a magneto-optical disk drive using a so-called magnetic super resolution (MSR) recording medium, a constant magnetic field has to be applied to the recording medium when reading data from the recording medium. In this case, using the above-mentioned drive circuit for the magnetic head, the power consumption during the data reading period can be reduced.
A first winding configuration of the magnetic head according to the present invention has a bifilar winding with a center tap and an additional winding element connected to each of the winding ends of the bifilar winding, so that four winding elements and five taps including the center tap and two end taps constitute the whole winding of the magnetic head.
According to a first configuration of the drive circuit using the above-mentioned first winding configuration of the magnetic head, the drive circuit magnetizes only the inner bifilar winding of the magnetic head during a first period in which a magnetic reversal occurs, and magnetizes the entire winding including the additional outer winding elements of the magnetic head during a second period in which a magnetic reversal does not occur. Thus, the magnetizing current is reduced during the period without a magnetic reversal.
Preferably, a second magnetizing voltage applied to the inner bifilar winding and the additional outer winding elements of the magnetic head during the second period is set lower than a first magnetizing voltage applied to the inner bifilar winding of the magnetic head during the first period. Thus, the power consumption can be further reduced. It is also preferable to perform the switching from the second magnetizing voltage to the first magnetizing voltage before the magnetic reversal.
According to a second configuration of the drive circuit using the above-mentioned first winding configuration of the magnetic head, the drive circuit magnetizes only the inner bifilar winding during the data writing period with a magnetic reversal, and magnetizes the entire winding including the additional outer winding elements during the data reading period.
A second winding configuration of the magnetic head according to the present invention has a bifilar winding with a center tap and an additional winding provided separately from the bifilar winding. The number of turns of the additional winding is larger than that of half of the bifilar winding.
According to a first configuration of the drive circuit using the above-mentioned second winding configuration of the magnetic head, the drive circuit magnetizes the bifilar winding of the magnetic head during a first period in which a magnetic reversal occurs, and magnetizes the additional separate winding during a second period in which a magnetic reversal does not occur. Thus, the magnetizing current is reduced during the period without a magnetic reversal so that the power consumption can be reduced.
Preferably, a second magnetizing voltage applied to the additional separate winding of the magnetic head during the second period is set lower than a first magnetizing voltage applied to the bifilar winding of the magnetic head during the first period. Thus, the power consumption can be reduced further. It is also preferable to perform the switching from the second magnetizing voltage to the first magnetizing voltage before the magnetic reversal.
According to a second configuration of the drive circuit using the above-mentioned second winding configuration of the magnetic head, the drive circuit magnetizes the bifilar winding of the magnetic head during the data writing period with a magnetic reversal, and magnetizes the additional separate winding during the data reading period.
Another configuration of the drive circuit comprises a first drive circuit for magnetizing only half of the winding selectively by supplying a first magnetizing current between the center tap of the bifilar winding and one of the winding ends, a second drive circuit for magnetizing the entire winding by supplying second magnetizing currents to the winding ends of the bifilar winding selectively, the second magnetizing currents being smaller than the first magnetizing current and having opposite directions from each other, and a circuit for controlling the first and the second drive circuits selectively in accordance with bit pattern of a binary signal to be recorded.